I will whip up an example when I get home.
So for now a bit of guess work.
Track 1 original clip
Track 2 original clip with track matte effect
Track 3 white text (titler)
Set track matte effect to track 3.
Now for clip in track 2: some kind of CC effect maybe Invert.
Draco, could you change your username, so that others do not think that you work for adobe? Thanks!
Thanks! I will give your blind guess a go